1. Field of the Invention
The present invention relates to a submarine observation apparatus for and a submarine observation system for transmitting submarine observation data through a submarine optical cable.
2. Description of Related Art
In a prior art submarine observation system, land terminal equipment transmits a light signal modulated with control signals to a plurality of submarine observation apparatus, and each of the plurality of submarine observation apparatus carries out light-to-electric conversion of the incoming light signal using an optical receiver. Each of the plurality of submarine observation apparatus then multiplexes observation information about each of the plurality of submarine observation apparatus and an electric signal to which the received light signal has been light-to-electric converted into a multiplexed signal, and converts the multiplexed signal into a light signal and transmits the light signal to the next submarine observation apparatus using an optical transmitter. An optical fiber cable is looped back at an end thereof so that a light signal outputted from the last-state submarine observation apparatus is sent back to the land terminal equipment (refer to patent reference 1, for example).
[Patent reference 1] JP, 7-202804,A (see pp. 6 and FIG. 1)
In the prior art submarine observation system constructed as mentioned above, each of the plurality of submarine observation apparatus needs to include an optical receiver for light-to-electric converting all of an incoming light signal into an electric signal, and an optical transmitter for multiplexing observation information and the electric signal into a multiplexed signal and for electric-to-light converting the multiplexed signal into a light signal. Therefore, the scale and cost of each of the plurality of submarine observation apparatus increases. The increase in the scale of each of the plurality of submarine observation apparatus results in an increase in the consumed electric current and hence an increase in the temperature of the inside of the sealed housing of each of the plurality of submarine observation apparatus, which are detrimental to the reliability of the components and circuitry of each of the plurality of submarine observation apparatus.
In another prior art submarine observation system having a point-to-point structure in which an optical transceiver unit of land terminal equipment is placed opposite to an optical transceiver unit of each of a plurality of submarine observation apparatus byway of one submarine optical cable for transmission of observation information, when a new submarine observation apparatus is added to the system, it is necessary to also add a submarine optical cable having a length similar to those of existing submarine optical cables. Therefore, the submarine observation system cannot be easily expanded.
In another prior art submarine observation system using a wavelength division multiplexing transmission method of multiplexing two or more fixed-wavelength light signals into a single optical fiber so as to transmit observation information, although the above-mentioned problem associated with the expandability is solved, high wavelength stability is required of optical transceiver units for wavelength division multiplexing transmission. In order to achieve this high wavelength stability, circuit devices, such as a Peltier control unit (i.e., a unit for controlling the temperature of a corresponding device using an element for converting electric power into heat in order to stabilize the oscillation wavelength), and a wavelength locker (i.e., a unit for locking the oscillation wavelength to a desired wavelength by monitoring the oscillation wavelength of an optical transmitter and controlling a wavelength filter and the temperature of the device), are required. As a result, the scale and cost of each of the plurality of submarine observation apparatus increases. The increase in the scale of each of the plurality of submarine observation apparatus results in an increase in the consumed electric current and hence an increase in the temperature of the inside of the sealed housing of each of the plurality of submarine observation apparatus, which are detrimental to the reliability of the components and circuitry of each of the plurality of submarine observation apparatus.